By coming out publicly, Cook "he committed himself to using the influence that comes with heading of one of the world's largest corporations to fight for the rights and equality of lesbian, gay, bisexual and transgender (LGBT) people across America," the group said in its statement.

Cook has previously spoken out about LGBT rights, but hadn't yet publicly come out as a gay man himself.

Human Rights Campaign President Chad Griffin said in a statement that Cook's announcement with "save countless lives."

"He has always been a role model, but today millions across the globe will draw inspiration from a different aspect of his life," Griffin said. "Tim Cook is proof that LGBT young people can dream as big as their minds will allow them to, whether they want to be doctors, a U.S. Senator, or even CEO of the world's biggest brand."

In his essay, Cook wrote that he's wanted to retain some personal privacy in his life, but that if his public coming out could "help someone struggling to come to terms with who he or she is, or bring comfort to anyone who feels alone, or inspire people to insist on their equality," then it's worth the privacy trade-off.

Here is the full statement from the Human Rights Campaign:

"Tim Cook's announcement today will save countless lives. He has always been a role model, but today millions across the globe will draw inspiration from a different aspect of his life. Tim Cook is proof that LGBT young people can dream as big as their minds will allow them to, whether they want to be doctors, a U.S. Senator, or even CEO of the world's biggest brand. Apple has consistently fought for the LGBT community and we're incredibly grateful that today's announcement will bring even more to their work for equality."